1. Field of the Invention
The present invention relates to an optical communication module in optical communication and, more particularly, to an optical communication module having a mirror which reflects a signal light and folds the same and a manufacturing method thereof.
2. Description of the Related Art
One of conventional optical communication modules having a mirror for reflecting a propagated light which is provided midway through an optical waveguide to couple the propagated light with a light-receiving element is, for example, the optical communication module disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 10-224310 which is illustrated in FIG. 10.
The conventional technique disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 10-224310 is intended to realize an optical communication module for conducting bidirectional communication using signal lights of the same wavelength by a small-sized and simple structure. In the structure, a Y-branch type optical waveguide is formed on an optical waveguide substrate, a mirror is provided midway through a branch side waveguide for reflecting a propagated light to the side of the surface of the optical waveguide substrate, a light-receiving element is provided facing the crossover portion between the one branch side waveguide and the mirror, and a light-emitting element is provided facing the crossover portion between the other branch side waveguide and the mirror.
Because an Y-branch type optical waveguide which can be formed minutely and to high precision is used on the optical waveguide substrate and the light-receiving element and the light-emitting element are enabled to be surface-packaged on the optical waveguide substrate, an optical communication module for conducting bidirectional communication using signal lights of the same wavelength can be realized with a small-sized and simple structure.
Another example is the conventional optical communication module for conducting bidirectional communication using two signal lights of different wavelengths, which is disclosed in Japanese Patent Laying-open (Kokai) No. Heisei 11-068705 and illustrated in FIG. 11.
The conventional art disclosed in Japanese Patent Laying-Open No. Heisei 11-068705 is intended to reduce crosstalk light which is leakage of an LD (laser diode) light as a transmitted light in a PD (photodiode) light as a received light down to a level causing no problem in practical use. In the module, an optical branch waveguide is formed on a plane substrate, a groove is provided at a branch portion of the optical branch waveguide, a dielectric multilayer filter for branching an input light into its penetration direction and a reflection direction according to its wavelength is inserted into the groove, and a transmission LD and a reception PD to be optically coupled with the optical branch waveguide are provided on the plane substrate.
With a penetration wavelength of the dielectric multilayer filter set to be as a reception wavelength of the reception PD and a blocking wavelength of the dielectric multilayer filter set to be as a transmission wavelength of the transmission LD and the transmission LD and the reception PD arranged at positions opposed to each other with the dielectric multilayer filter provided therebetween, bidirectional WDM (wavelength division multiplexing) optical communication is conducted.
A further example of conventional optical communication modules is disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 11-237529, which is illustrated in FIG. 12.
The optical communication module according to the conventional technique disclosed in Japanese Patent Laying-Open No. Heisei 11-237529 has a structure in which with a buffer and a clad formed on the upper surface of an Si substrate to have slant surfaces, a signal light is folded upward and received by a PD by making the use of reflection caused by a difference in refractive indexes between air on the slant surfaces and the clad.
The above-described conventional optical communication modules, however, have the following problems.
First, with conventional optical communication modules having a groove of a small width, because of a structure in which a mirror and a filter are inserted into the narrow groove, much labor is cost for their manufacturing and moreover, automation of a manufacturing process is difficult, which make manufacturing costs extremely high.
Because the conventional art disclosed in Japanese Patent Laying-Open No. Heisei 10-224310, for example, has a structure in which a mirror is inserted into a groove formed slantwise and the conventional art disclosed in Japanese Patent Laying-Open No. Heisei 11-068705 has a structure in which a dielectric multilayer filter is inserted into a groove provided at a branch portion of an optical branch waveguide, both require extremely laborious work for inserting the filter or the like into a narrow groove.
Secondly, the conventional optical communication modules in which a signal light penetrating a filter at a groove portion is received by a PD need a groove to be formed to have an extremely small width in order to suppress loss of a received signal light at the groove portion. For this purpose, as a dielectric multilayer filter to be inserted, a filter whose material is thin and soft such as polyimide should be used, which makes handling of the filter at its insertion be worse than that of a filter of a hard material to make automation of a filter insertion process difficult.
Thirdly, in the conventional optical communication modules which output a signal light reflected on a filter at a groove portion from an optical waveguide to an external optical fiber, because a slant of the filter relative to an end surface of the waveguide largely affects coupling characteristics between a reflected light on the filter and the optical waveguide, the filter should be inserted very carefully so as not to slant relative to the end surface of the waveguide, whereby reduction in assembly costs is difficult.
Fourthly, the conventional optical communication modules in which a signal light is reflected from inside a substrate and received by a PD disposed on the surface of the substrate, which make the use of reflection caused by a difference in refractive indexes between air and a clad for the reflection of the signal light, need air within a groove portion having a reflection surface. In a case, for example, where an optical communication module is covered with a transparent resin or the like, because a refractive index of a transparent resin is closer to that of a clad than to that of air, reflection on a slant surface might not be obtained. Therefore, use of simplified sealing by transparent resins and use of packaging realized by protecting an optical system with transparent resins and by molding the entire system are impossible, resulting in limiting packaging methods.